The present invention relates to a die for driving a pierce nut into a metal panel for clinch interconnection.
The use of a pierce nut is one way of forming an internal thread in a pressed sheet metal. At the time of pressing metal, a pierce nut is pressed against a metal panel so that its punching portion pierces the metal panel, forming a bolt aperture, and at the same time, the nut itself is attached to the metal panel by clinching. For clinch interconnection of the pierce nut to the metal panel, as shown in FIG. 4, a die for driving a pierce nut is set first. An annular coining portion 2 having its inner surface continuous to a center aperture 3 is provided on the top of a die body 1 of the die. A metal panel 10 is then placed on the annular coining portion 2 on the top of this die, and, a pierce nut 20 is driven into the straight center aperture 3 from above the metal panel 10 by a punch 30 to pierce the metal panel 10 by shearing between the outer surface of the pierce nut 20 (punch portion 22 of the nut) and the annular coining portion 2 on the top of the die. At the same time, the pierce nut 20 is attached to the metal panel 10 by clinching.
The center aperture 3 of the conventional pierce-nut driving die of this type has a straight surface so that debris 11 is merely held by frictional force. When the metal panel is lifted from the die body by a lifting load, the debris is lifted together with the metal panel and is put on the top of the die body, which is likely to stand in the way of a continuous driving work or damage the die. These sort of troubles are often observed in a clinching operation using thin metal panels of 1 mm thickness or thinner.
In an ordinary punch-die set, there is small clearance between the punch and the die aperture, and it is possible to provide a large amount of overlapping of the punch into the die aperture during a piercing operation of the metal panel. The debris is therefore pushed down to the relief portion of the die aperture (the aperture portion with an increased diameter where the debris can fall freely) so that the debris easily falls down. In the case of a pierce nut, however, such a situation is not expected due to structural as well as manufacturing restrictions.